Surface engraver

ABSTRACT

A machine for engraving surfaces which may be cylindrical, tapered or curved from a pattern which lies in a flat plane. The article to be engraved is rotated about its longitudinal axis at different speeds by frictional contact between a sheave and a stationary rod as the sheave and article are translated in direction parallel to the longitudinal axis of said rod.

United States Patent 1191 Varga July 15, 1975 SURFACE ENGRAVER 3,578,388 6/1971 Muehlenweb JO/13.6 x 3664,20 51972 M h ..90l .6X [75] Inventor: Franz Varga, Murten, Switzerland 3 ec amc 3 [73] Assignee: New Hermes Engraving Machine P i E i r Gil Weidenfeld Corporatilm, New York, NY Attorney, Agent, or Firm-Seidel, Gonda & 22 Filed: June 17, 1974 Goldhammer 21 A LN 479,723 1 PP 57 ABSTRACT [52] U S. C] 90/13 90/13 33/22 A machine for engraving surfaces which may be cylin- [51] Int. Cl. n 1/18 drical, tapered or curved from a pattern which lies in [58] Field 6 l3 I a flat plane. The article to be engraved is rotated about its longitudinal axis at different speeds by frictional contact between a sheave and a stationary rod as the sheave and article are translated in direction [56] g nfi gif parallel to the longitudinal axis of said rod.

1,889,660 11 1932 Homer 33 22 x 12 Claims, 3 Drawing Figures SURFACE ENGRAVER This invention relates to engraving machines and more particularly to machines which can engrave surfaces which may be cylindrical, tapered or curved by following patterns which lie in a fiat plane such as that disclosed in application Ser. No. 381,967 filed on July 23, 1973 by Edwin Sprenger, entitled CURVED SUR- FACE ENGRAVER, and now US. Pat. No. 3,830,136.

The engraving apparatus comprises a pattern to be engraved and an engraving tool for engraving the pattern on an article. A means is connected between the tool in the pattern and includes a follower which traces the pattern. A first means supports an article to be engraved for translation in mutually perpendicular first and second directions. A second means rotates the article about an axis parallel to said first direction as the article is translated along the second direction.

The second means includes a shaft which is parallel to said first direction. An annular member is coupled to said shaft. A stationary rigid rod is in frictional contact with the annular member. A means is provided to adjust the speed of rotation of the annular member as the annular member and said shaft are translated in said second direction.

In a specific embodiment of the present invention, the annular member is sheave comprised of two components movable toward and away from one another. The means for adjusting the speed of rotation of the annular member includes a support for the rod which is adjustable in a manner whereby the location of frictional contact between the rod and the sheave is adjustable in a direction toward and away from the longitudinal axis of the sheave.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a perspective view of engraving apparatus incorporating the present invention.

FIG. 2 is an elevation view taken along the line 2-2 in FIG. 1.

FIG. 3 is a sectional view taken along the line 3-3 in FIG. 2.

Referring to the drawing in detail, wherein like numerals indicate like elements, there is shown in FIG. 1 an engraving apparatus incorporating the present invention and designated generally as 10.

Apparatus comprises a base frame 12, engraving tool device 14, means for coupling the engraving tool device 14 to the frame 16, a pattern support 18 for supporting a pattern in a flat plane and means 20 for following a pattern on the pattern support. The following means 20 is connected to the frame 16 by a suitable element 22.

The pattern comprised of letters 172 is supported in a fiat plane on the pattern support 18 and is adapted to mounted on guide plate 34 for movement along a first path which is indicated by the arrow 38. The coupling means also includes a second slide plate 40. The second slide plate 40 is mounted on slide plate 36 for movement along a second path indicated by arrow 42.

First and second paths 38 and 42 are mutually perpendicular to each other so that an object may be moved to any desired location with respect to the base frame 12. The second slide plate 40 can be constrained by raised bearing tracks on the surface of slide plate 36 or by any other suitable means. Further, the paths of movement of the two slide plates 36, 40 could be reversed without departing from the scope or spirit of the be engraved on the curved surface 26 of the article 28.

The base frame 12 may comprise a plurality of legs 32 which may rest on a suitable support such as a table or V the like. A guide plate 34 which is an elongated rectangular member is supported on the base frame 12 by being connected to plate 35 which in turn is supported on the base frame 12.

The means for coupling the engraving tool device 14 to the frame 16 comprises a slide plate 36 which is an elongated rectangular member. Slide plate 36 is invention.

An upright element 46 is supported on the upper surface of slide plate 40 for movement therewith. The upright element 46 has an upwardly facing elongated central opening 48. A block 56, which is constrained in the central opening 48 for vertical movement relative to the surface of slide plate 40, supports the engraving tool device 14 for vertical movement and for rotation in a manner which will be described in greater detail herein.

The block 56 may be moved verticaly in a number of convenient ways. However, a presently preferred apparatus comprises a rack and pinion arrangement wherein the rack 58 is fixed to block 56 while the pinion 60 is secured to upright element 46 by a pin 62 and is rotated about that pin by a lever 64. A knob 65 may be positioned at the end of lever 64.

The block 56 may be constrained in its full raised position by a suitable detent. Preferably, the detent comprises a second lever 66 which is connected at an intermediate portion thereof to an intermediate portion of lever 64 by a pin. One end of lever 66 is adapted to rest beneath an outwardly extending ledge 70 on the upright element 46 when the block 56 is in its full raised position. Lever 66 prevents lever 64 from rotating counterclockwise to permit block 56 to descend. The second lever 66 maybe disengaged by merely raising block 56 above the position indicated and rotating the second lever 66 out from under ledge 70.

The block 56 includes a hollow boss. A hollow bearing support is mounted within the boss and rotatably supports an elongated shaft 78 so that the shaft can rotate about its own longitudinal axis. The longitudinal axis of shaft 78 is parallel to the first path of movement 38. A generally goose-neck shaped arm 84 is fixed to the end of shaft 78 for rotation therewith. The arm 84 may be connected'to the shaft 78 by a set screw or by any other convenient means.

The goose-neck shaped arm 84 has a first forwardly extending portion, an upwardly and forwardly extending portion and a second forwardly extending portion 94. The engraving tool device 14 includes an engraving tool holder 98 which is supported at the end of the second forward portion 94. The engraving tool is supported in the engraving tool holder 98 so that its cutting face lies along an extension of the longitudinal axis of shaft 78 between first and second guide arms 104. The guide arms 104 are supported by the goose-neck shaped arm 84.

The engraving tool holder 98 is well known in the art. It comprises a chuck in which the engraving tool is recieved. The chuck can be raised and lowered inside the tool holder by pivoting lever 105 connected by linkage 3 to the chuck. The chuck has a sheave 1 11 so that it can be driven.

A motor 108 and counterweight are supported at the opposite end of shaft 78. The motor 108 is connected to engraving tool holder 98 by virtue of an elongated flexible member such as a belt 112 which engages sheave ll 1 on the chuck and sheave 114 on the motor drive shaft.

Slide plate 36 supports first and second adjustment plates 116 and 118. Both plates 116, 118 are fixed to each other and to slide plate 36 for movement therewith. Plate 116 is fixed to slide plate 36 and has a gear supported in a recess therein at the end of shaft 122. A knob 124 at the free end of shaft 122 enables the gear to be turned.

Plate 118 has an elongated recess which is disposed in parallel relation to direction of travel indicated by arrow 42. The plate 118 has an opening through which a portion of the gear on shaft 122 may extend. A threaded shaft 127 having a knob 128 is threadingly received in plate 118.

The article 28 whose surface 26 is to be engraved is mounted between the jaws of scroll chucks 132 and 134. The chucks 132, 134 include mandrels which are rotatably mounted on one of the jaws 140 and 142. The jaws 140 and 142 are slidably mounted on an elongated member 144 which is received in plate 118. Elongated member 144 is dovetailed so that the jaws are constrained for sliding movement thereon along the path defined by arrow 42. Member 144 has a rack on its lower surface that is engaged with a gear attached to shaft 122 so that displacement of member 144 in a longitudinal direction relative to plate 118 can be easily achieved. Knob 128 and shaft 127 lock member 144 in any desired position.

The jaws 140, 142 are mounted in facing relation to each other on member 144. Member 144 is provided with an elongated threaded shaft 146 which may be rotated by a crank handle 148. The jaws 140 and 142 are engaged by the threads in shaft 146 so that rotation of the handle 148 moves the jaws 140, 142 toward and away from each other on member 144.

Significantly, it should be noted that the engraving tool lies along a radius extending from the axis of rotation of the scroll chucks 132, 134. Furthermore, both the engraving tool and the scroll chucks are supported for movement on slide plates 36. Thus, as slide plate 36 is displaced along guide 34 in the direction of arrow 38, the engraving tool always remains over said axis of rotation. However, the article 28 to be engraved is rotated so that a different portion of the surface 26 thereof is beneath the engraving tool as the slide plate 36 is moved.

The pattern supporting means 18 lies in a flat plane above the article to be engraved. As illustrated it may be supported by one or more arms 169 which are connected to the base frame 12. A bracket 171 on the pattern support 18 carries the pattern to be engraved. The pattern may typically comprise letters 172.

The following means 20 may comprise a pantograph:

device 170 which includes a follower element 173 so that the movements of the follower element 173 are transmitted to upright element 46 by way of element 22 and pin 174. The pantograph device 170 is supported by legs 175, 177 above the elevation of the engraving tool device 14.

The pantograph device illustrated herein is well known in the art and need not be described in detail. However, as indicated above the pantograph device 170 andthe pattern support 18 are carried by the base frame 12in overlying relation to the article 28 to be engraved. However, this arrangement is not critical since any convenient form of coupling between the pantograph device 170 and the upright element 46 could be employed.

As is well known, the movement of the follower element 173 in the plane of pattern support 18 can be resolved into two components. These components are useful in transferring the movement of the follower element 173 to slide plates 36 and 40. One of the components may be identified as a third path which is defined by arrow 176. The other component is identified as a fourth path which is defined by arrow 178. Both the third and four paths are mutually perpendicular to each other and correspond to the first and second paths respectively.

Thus, movement of the follower element 173 along third path 178, causes slide plates 36 and 40 to move along the first path in the direction of arrow 38. Movement of follower element 173 along the fourth path in the direction of arrow 178 causes slide plate 40 to move along the second path relative to slide plate 36.

The apparatus 10 includes means for rotating the article 28 as the article 28 is translated along the first path defined by arrow 38. The means for causing such rotation of the article 28 about its longitudinal axis includes shaft 180. Shaft 180 has one end connected to the chuck 132 and is rotatably supported by the jaw 140. The other end of shaft 180 is connected to and rotatably driven by a sheave designated generally as 182.

Sheave 182 is rotatably driven by frictional contact with a rigid rod 183 as the article 28 is translated along the first path in the direction of arrow 38. Rod 183 is supported in cantilever by a U-shaped bracket having a guide 184. Guide 184, by means of a set screw or the like, facilitates horizontal adjustment of rod 183 in a direction parallel to the arrow 42. The guide 184 and its bracket are secured to a sleeve 185. Sleeve 185 is vertically adjustable along the vertical leg 177 which cooperates with leg 175 to support the pantograph device 170. A handle 186 is provided to facilitate locking the sleeve 185 to the leg 177 in any desired elevation.

The sheave 182 is comprised of first and second sheave members 188 and 196. The sheave member 188 is provided with a beveled surface 190 adjacent its periphery and a radially inwardly directed surface 192. See FIG. 3. Sheave member 188 has a boss 194 surrounding shaft 180 and is keyed or otherwise coupled thereto so that rotation of sheave member 188 rotatably drives shaft 180.

The sheave member 196 has threads on its inner periphery in mating engagement with threads on the outer periphery of the boss 194. Sheave member 196 has a face which mates with and is juxtaposed to the surfaces 190, 192, for frictional contact with opposite sides of the rod 183. The position of sheave member 196 along the boss 194 is r eadily adjustable and may be fixed in any convenient manner such as by a set screw whereby the space I between the juxtaposed surfaces on the sheave members 188, 196 may be varied as a function of the diameter .or curvature of the surface 26 on the article 281to; be engraved. Thus, when changing from one size article 28 to another size article 28, the only adjustment necessary to compensate of sheave member 196 with respect to sheave member 188 after first loosening handle 186. Thereafter, handle 186 will be tightened.

A journal 198 is supported by bearing 202 on shaft 180. A second journal 200 is supported by bearing 204 on shaft 180. The sheave 182 is between the journals 198, 200.

A mounting post 206 is vertically disposed with its lower end threaded to or otherwise connected to the journal 198. A similar mounting post 208 is connected to the journal 200. A nonrotatable shaft 210 is provided parallel to shaft 180 and directly above shaft 180. See FIG. 3. Shaft 210 has a flat 212 on one end and a flat 214 on the other end. Mounting post 206 extends through a hole in the shaft 210 at the flat 212. Mounting post 208 extends through a hole in the shaft 210 at the flat 214.

A spring 216 surrounds post 206 and extends between a nut and washer at the upper end of post 206 and a washer juxtaposed to the flat 212. A spring 218 is similarly associated with the post 208. The springs 216 and 218 bias the shaft 210 downwardly toward the shaft 180.

An annular retainer 220 is rotatably supported on a central portion of the shaft 210 between the flat 212, 214 by means of a bearing 222. The outer periphery of the retainer 220 is concave and frictionally embraces the rod 183. Retainer 220 under the bias of springs 216, 218 biases the rod 183 downwardly to any predetermined horizontal elevation wherein rod 183 is in frictional contact with the mating faces of the sheave members 188, 196.

In any convenient location, a pointer and scale is provided for indicating the relative position of the sheave members 188, 196 as a function of the diameter of the article 28 to be engraved. As illustrated, pointer 224 is supported by shaft 210 and cooperates with graduations 226 on the journal 200. As shown in FIG. 2, the sheave 182 has been preset to engrave article 28 which has a diameter of 4V2 inches. As the diameter of the article 28 changes, it is necessary to adjust the sheave 182 so that the article 28 rotates about its longitudinal axis with the proper surface speed.

The rod 183 is supported by the structure described above for movement in a direction toward and away from the longitudinal axis of shaft 180 which coincides with the axis of rotation of article 28. Since the guide 184 is parallel to the longitudinal axis of threaded shaft 146, rotation of shaft 146 to adjust the position between the jaws 140 and 142 does not in any way interfere with the relationship between the rod 183 and the sheave 182.

In order to engrave a surface 26, the desired pattern letters 172 are placed within bracket 171 on pattern support 18. Because the pattern support 18 is flat, it is not necessary to use specially prepared pattern pieces as those which have been used for conventional engraving on flat surfaces may be employed. The article 28 to be engraved is positioned within the scroll chucks 132 and 134. The jaws 140, 142 are then clamped on the ends of article 28 by rotating crank handle 148.

Knob 124 is rotated to move elongated member 144 and the article 28 longitudinally so that the portion of the surface 26 to be engraved is under the engraving tool. Knob 128 is rotated to lock elongated member forthe difference A in diameter between the articles is to adjust the position 144 against further movement. The engraving tool is then lowered by counterclockwise rotation of lever 105 until its cutting face engages surface 26. The weight of the tool, shaft 78, motor 108 and counterweight 110 tracing the horizontal portions of the letter B the article 28 rotates about its axis thereby permitting the tool to engrave corresponding parts of the letter on surface 26. This is accomplished because the coupling element 22 causes slide plate 36 to move along the first path in the direction of arrow 38. However, because sheave 182 is in frictional contact with stationary rod 183, the sheave 182 and article 28 coupled thereto are caused to rotate.

On the other hand, when the follower element 17 3 moves along the fourth path in the direction of arrow 178 as, for example, when by tracing the vertical part of the letter B the coupling element 22 causes the slide plate 40 to move along the second path in the direction of arrow 42 thereby translating the engraving tool along the axis of the article 28.

It is apparent that the letters 172 of the entire pattern which are to be reproduced can be covered by a combination of movements corresponding to the direction of the third and fourth paths. These movements are translated by the apparatus disclosed herein to rotary movement of the article 28 to be engraved under the engraving tool and translation of the engraving tool relative to the article 28. The guide arms 104 and the cutting face of the engraving tool define a plane so that the engraving tool is always perpendicular to the surface 26 which is to be engraved. Thus, uniform engraving of high quality may be achieved herein.

It should be noted that the pattern support and pantograph device have been shown positioned so that the first path and third path are parallel, and the second path and fourth path are also parallel. This results in a simple arrangement for coupling the panto graph device 170 to the engraving tool. However, the pattern to be traced thereby can be in any convenient position with respect to the engraving tool providing a suitable linkage is provided for transferring movements along the third and fourth paths of the follower elements 173 to corresponding movements along the first and second paths of the slide plates 36 and 40.

While the invention has been described with reference to a particular embodiment thereof, it should be apparent that many other forms and embodiments of the invention would be obvious to persons skilled in the art. Accordingly, the scope of the invention should not be limited by the foregoing description, but rather, only by the scope of the claims appended hereto.

It is claimed:

1. Engraving apparatus comprising a pattern to be engraved, an engraving tool for engraving an article with at least 'a portion of said pattern, means connected between said tool and pattern including means for following the pattern, first means for supporting an article to be engraved for translation in mutually perpendicular first and second directions, second means for rotating the article about an axis parallel to said first direction as the article is translated in the second direction, said second means including a rotatable shaft having its longitudinal axis parallel to said first direction, an annular member coupled to said shaft to rotate the shaft, a stationary rigid rod being retained in frictional contact with said annular member to cause rotation of said annular member when translated in said second direction, the longitudinal axis of said rod being perpendicular to the axis of said shaft, and means to adjust the speed at which said rod rotates said annular member when said annular member and shaft are translated in said second direction.

2. Apparatus in accordance with claim 1 wherein said speed adjusting means changes the location of contact of said rod with said annular member relative to the longitudinal axis of said shaft.

3. Apparatus in accordance with claim 2 wherein said annular member is a sheave defined by first and second sheave members which are coaxial with respect to said shaft, said sheave members having juxtaposed faces, one sheave member being mounted for movement toward and away from the other sheave member to adjust the distance between said juxtaposed faces.

4. Apparatus in accordance with claim 1 including a retainer in rolling contact with said rod for biasing said rod into frictional contact with said annular member.

5. Apparatus in accordance with claim 1 wherein said annular member is comprised of first and second sheave members having mating faces which are at least in part beveled surfaces converging toward the axis of said shaft, and means for adjusting the position of one sheave member with respect to the other sheave member for changing the location of frictional contact between said sheave members and said rod with respect to the longitudinal axis of said shaft for changing the speed of rotation of said shaft as the shaft is translated in said second direction.

6. Apparatus in accordance with claim 5 including a pointer and a graduated scale for indicating the relative position of one sheave member with respect to the other.

7. In an engraving apparatus comprising a first means for supporting an article to be engraved and mounted for movement in mutually perpendicular first and second directions, a second means associated with said first means for rotating an article about an axis which is parallel to said first direction as the article is translated in the second direction, said second means including a shaft rotatable about its longitudinal axis parallel to said first direction, a rigid rod parallel to said second direction, a sheave drivingly coupled to said shaft and being retained in frictional contact with said rod to cause rotation of said sheave when translated in said second direction, and means for adjusting the location of frictional contact between said rod and sheave with respect to the longitudinal axis of said shaft for changing the speed of rotation of said shaft.

8. In apparatus in accordance with claim 7 wherein said second means includes a retainer supported for rotation about an axis parallel to said shaft, said retainer being in frictional contact with said rod, and means for biasing said retainer and rod into frictional contact between said sheave at a predetermined distance from the axis of rotation of said shaft.

9. In apparatus in accordance with claim 8 including means for guiding said shaft for reciprocation in a direction parallel to said first direction and for adjusting the elevation of said rod in a third direction which is perpendicular to each of said first and second directions.

10. In apparatus in accordance with claim 9 wherein said sheave is comprised of first and second mating halves, and means for adjusting the distance between said mating halves, with at least a portion of the juxtaposed surfaces on said mating halves being a beveled surface converging toward the axis of said shaft.

11. In engraving apparatus comprising jaw means for supporting and rotating an article to be engraved about its longitudinal axis, said jaw means including a shaft being coaxial with the axis about which the article is to be rotated, a sheave drivingly coupled to said shaft and said sheave being defined by first and second sheave members, means for adjusting one sheave member toward and away from the other sheave member for changing the location of frictional contact of said rod with said sheave members relative to the axis of rotation of said sheave members, and means for moving said sheave members in a direction parallel to the longitudinal axis of said rod so that frictional contact with said rod drives said sheave members at different rotational speeds as a function of the distance of said rod from the axis of rotation of said sheave members.

12. In apparatus in accordance with claim 1 including a retainer rotatably supported about an axis perpendicular to the longitudinal axis of said rod, said retainer being in frictional contact with said rod for maintaining said rod in frictional contact with said sheave members, and means biasing said retainer toward the longitudinal axis of said rod. 

1. Engraving apparatus comprising a pattern to be engraved, an engraving tool for engraving an article with at least a portion of said pattern, means connected between said tool and pattern including means for following the pattern, first means for supporting an article to be engraved for translation in mutually perpendicular first and second directions, second means for rotating the article about an axis parallel to said first direction as the article is translated in the second direction, said second means including a rotatable shaft having its longitudinal axis parallel to said first direction, an annular member coupled to said shaft to rotate the shaft, a stationary rigid rod being retained in frictional contact with said annular member to cause rotation of said annular member when translated in said second direction, the longitudinal axis of said rod being perpendicular to the axis of said shaft, and means to adjust the speed at which said rod rotates said annular member when said annular member and shaft are translated in said second direction.
 2. Apparatus in accordance with claim 1 wherein said speed adjusting means changes the location of contact of said rod with said annular member relative to the longitudinal axis of said shaft.
 3. Apparatus in accordance with claim 2 wherein said annular member is a sheave defined by first and second sheave members which are coaxial with respect to said shaft, said sheave members having juxtaposed faces, one sheave member being mounted for movement toward and away from the other sheave member to adjust the distance between said juxtaposed faces.
 4. Apparatus in accordance with claim 1 including a retainer in rolling contact with said rod for biasing said rod into frictional contact with said annular member.
 5. Apparatus in accordance with claim 1 wherein said annular member is comprised of first and second sheave members having mating faces which are at least in part beveled surfaces converging toward the axis of said shaft, and means for adjusting the position of one sheave member with respect to the other sheave member for changing the location of frictional contact between said sheave members and said rod with respect to the longitudinal axis of said shaft for changing the speed of rotation of said shaft as the shaft is translated in said second direction.
 6. Apparatus in accordance with claim 5 including a pointer and a graduated scale for indicating the relative position of one sheave member with respect to the other.
 7. In an engraving apparatus comprising a first means for supporting an article to be engraved and mounted for movement in mutually perpendicular first and second directions, a second means associated with said first means for rotating an article about an axis which is parallel to said first direction as the article is translated in the second direction, said second means including a shaft rotatable about its longitudinal axis parallel to said first direction, a rigid rod parallel to said second direction, a sheave drivingly coupled to said shaft and being retained in frictional contact with said rod to cause rotation of said sheave when translatEd in said second direction, and means for adjusting the location of frictional contact between said rod and sheave with respect to the longitudinal axis of said shaft for changing the speed of rotation of said shaft.
 8. In apparatus in accordance with claim 7 wherein said second means includes a retainer supported for rotation about an axis parallel to said shaft, said retainer being in frictional contact with said rod, and means for biasing said retainer and rod into frictional contact between said sheave at a predetermined distance from the axis of rotation of said shaft.
 9. In apparatus in accordance with claim 8 including means for guiding said shaft for reciprocation in a direction parallel to said first direction and for adjusting the elevation of said rod in a third direction which is perpendicular to each of said first and second directions.
 10. In apparatus in accordance with claim 9 wherein said sheave is comprised of first and second mating halves, and means for adjusting the distance between said mating halves, with at least a portion of the juxtaposed surfaces on said mating halves being a beveled surface converging toward the axis of said shaft.
 11. In engraving apparatus comprising jaw means for supporting and rotating an article to be engraved about its longitudinal axis, said jaw means including a shaft being coaxial with the axis about which the article is to be rotated, a sheave drivingly coupled to said shaft and said sheave being defined by first and second sheave members, means for adjusting one sheave member toward and away from the other sheave member for changing the location of frictional contact of said rod with said sheave members relative to the axis of rotation of said sheave members, and means for moving said sheave members in a direction parallel to the longitudinal axis of said rod so that frictional contact with said rod drives said sheave members at different rotational speeds as a function of the distance of said rod from the axis of rotation of said sheave members.
 12. In apparatus in accordance with claim 1 including a retainer rotatably supported about an axis perpendicular to the longitudinal axis of said rod, said retainer being in frictional contact with said rod for maintaining said rod in frictional contact with said sheave members, and means biasing said retainer toward the longitudinal axis of said rod. 